Improve error messaging for module submission.

Fixes: https://pagure.io/fm-orchestrator/issue/1098

module_build_service/common/scm.py

@@ -333,11 +333,12 @@ class SCM(object):
             with open(path_to_yaml):
                 return path_to_yaml
         except IOError:
-            log.error(
+            msg = (
                 "get_module_yaml: The SCM repository doesn't contain a modulemd file. "
                 "Couldn't access: %s" % path_to_yaml
             )
-            raise UnprocessableEntity("The SCM repository doesn't contain a modulemd file")
+            log.error(msg)
+            raise UnprocessableEntity(msg)
 
     @staticmethod
     def is_full_commit_hash(scheme, commit):

module_build_service/web/views.py

@@ -522,8 +522,9 @@ class SCMHandler(BaseHandler):
             raise Forbidden("The submitted scmurl %s is not allowed" % url)
 
         if not get_scm_url_re().match(url):
-            log.error("The submitted scmurl %r is not valid" % url)
-            raise ValidationError("The submitted scmurl %s is not valid" % url)
+            msg = "Expected format is '%s?[module-path]#[revision]'" % url
+            log.error("The submitted scmurl %r is not valid.  %s" % (url, msg))
+            raise ValidationError("The submitted scmurl %s is not valid.  %s" % (url, msg))
 
         if not skip_branch and "branch" not in self.data:
             log.error("Missing branch")

tests/test_web/test_views.py

@@ -1239,7 +1239,9 @@ class TestSubmitBuild:
         data = json.loads(rv.data)
         assert data["message"] == (
             "The submitted scmurl https://src.stg.fedoraproject.org"
-            "/modules/testmodule.git is not valid"
+            "/modules/testmodule.git is not valid.  Expected format is "
+            "'https://src.stg.fedoraproject.org/modules/testmodule.git?"
+            "[module-path]#[revision]'"
         )
         assert data["status"] == 400
         assert data["error"] == "Bad Request"